This invention pertains to a method of synthesizing organic prepolymers, and, more particularly, to an improved method of synthesizing bisorthodinitriles using a dipolar aromatic solvent as the reaction medium.
Current methods of synthesizing bisorthodinitriles and the cyanocondensation resins prepared therefrom have been detailed, for example, in U.S. Pat. Nos. 3,993,631; 4,056,560; 4,057,569; 4,067,860 and 4,116,945. The references: 4,057,569 and 4,116,945 disclose that disorthodinitriles of the generic formula: ##STR2## wherein R is an aliphatic or aromatic radical can be prepared by reacting 4-aminophthalonitrile with the appropriate di-aldehyde in a refluxing solvent, such as benzene, toluene, chlorobenzene, anisole, or the like. The synthesis involving terephthaldehyde proceeds as follows:
This reaction, however, is flawed by the fact that a great amount of solvent is required in order to produce a small amount of the bisorthodinitrile, since large amounts of these solvents are required to dissolve the reactants. This necessitates large size reaction vessels, which leads to a very cumbersome production method. An even more serious flaw is that the reaction is a very slow one, often taking several days to produce product yields in the area of 35%.